Seized Perkins M30 Engine

Any experience\expertise welcome

Hi all,  

Found that our engine would not pass TDC on piston 3 when we lifted in last week, after being on the hard for the winter! On removal of the head showed piston 3 having debris of some sort as shown below.  

They are going to clean out the cylinder tomorrow and see how the piston and its rings travel in the bore with oil film, then the big decision will have to be made, either  

Get the head cleaned and checked (although will the bore be ok, are boat refits successful) 

Get the full engine fully stripped down (will it cost be as much as new engine) 

Get secondhand engine, Volvo 2030 being almost identical (more problems maybe...) 

Get a new engine, Volvo 1D-30 or another. (Cost, engine bay changes and which engine, higher HP?) 

If anyone has experience or expertise in this, I would be very welcome of any advice on the option above, also if debris in the cylinder/head suggest either sea water or coolant? How can there be so much debris in the cylinder? 

The Perkins M30 is fitted in a Rival 36, with a flexofold prop, with Hurst 100 gearbox. There was white smoke in later of the last season and when you started, the initial exhaust looked to be dirty and leave oily film on the water.  

It's been suggested that the water got in via the exhaust, due to the siphon break not working and water being siphoned in after the engine is turned off and entering the cylinder via the exhaust port. The other two cylinders look clean to me for a 30year old engine...